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1.
A Multiple-Tool Approach to Rough Machining of Sculptured Surfaces   总被引:2,自引:1,他引:1  
This paper proposes a methodology by which machining instructions can be generated directly from the 3D point data derived from either contact or non-contact measuring devices. Starting with the creation of a B-spline surface model from the 3D point data, several algorithms are developed to automate the generation of process plans, which contain detailed information needed for NC machining processes. In particular, the following issues are considered: 1. Use of ordered data points to fit a smooth surface. 2. Automatic selection of multiple cutting tools. 3. Generation of cutter-paths for rough machining. A cubic non-uniform B-spline (NUB) mathematical model is used for fitting measured data points into a smooth surface. For process planning based on the surface model, the selection and optimisation of cutting tools are based upon the criteria of maximum material removal and minimum tool change, while the generated NC cutter path ensures fast machining and the required surface quality.   相似文献   

2.
Path planning of multi-patched freeform surfaces for laser scanning   总被引:2,自引:1,他引:1  
In this paper, a new method for scanning a complex surface model with multiple patches is proposed. In scanning of freeform-shaped models, it is difficult to generate a measuring plan by human intuition due to the complexity of the part. The developed method calculates the number of scans, scan direction, and scan path for a stripe-type laser scanner. The user can designate the surface patches that need to be scanned. In generating the scan plan, surface information is first extracted from the CAD model automatically. Other information such as, design knowledge, functionality and machine parameters are provided interactively. Based on this information, the original surface model is sampled in the u, v parameter domain and the sampled points are grouped using the view angle of the laser scanner. The scan direction is determined by calculating the global mean vector of the sampled points that belong to a group. The range of the view angle can be varied to enhance the quality of captured point data. The optical scan paths for each scan direction are calculated by projecting the sampled points onto a 2D plane. The optical constraints are also verified to guarantee the generated scan plan.  相似文献   

3.
Complex surface inspection requires the optimal localization of the measured surface related to the design surface so that the two surfaces can be compared in a common coordinate frame. This paper presents a new technique for solving the localization problem. The basic approach consists of two steps: 1) rough localization of the measured points to the design surface based on curvature features, which can produce a good initial estimate for the optimal localization; 2) fine localization based on the least-square principle so that the deviation between the measured surface and the design surface is minimized. To efficiently compute the closest points on the design surface of the measured points, a novel method is proposed. Since this approach does not involve an iterative process of solving non-linear equations for the closest points, it is more convenient and robust. The typical complex surface is used to test the developed algorithm. Analysis and comparison of experimental results demonstrate the validity and applicability of the algorithm.  相似文献   

4.
Reverse engineering is an approach for constructing a CAD model from a physical part through dimensional measurement and surface model. For sheetmetal parts, when removed from dies after forming, are subject to springback due the resultant in-plane forces and moments throughout the sheet at the end of the forming processing. Therefore, springback should be compensated for integrating reverse engineering into the system of forming sheet metal with a complex surface. However, CAD modelling from measured points data is a roadblock to the automation of the duplication procedure. The difficulties here arise from surfaces fitting to measured points, which is well-known to be time-consuming. To avoid the roadblock, based on the convex hull property of B-spline, a new strategy for direct generation of die shapes from digitized points with springback compensation is presented in this paper. The proposed algorithm has been applied to a part of complicated geometry with good results.  相似文献   

5.
Given only a set of points, without any geometric information such as the adjacency among the points, the scanning order or the scanning direction, it is a difficult problem to reconstruct a surface model corresponding to the original shape. For the reconstruction of open shapes, many effective approaches have been proposed. It is, however, hard to find a robust and effective method for the reconstruction of closed shapes. In this paper, an algorithm is proposed to reconstruct a three-dimensional closed shape from a set of good sample points using the properties of Delaunay triangulation and Voronoi diagrams. The proposed method consists of three steps; (1) constructing a convex hull consisting of mutually exclusive tetrahedra by 3D Delaunay triangulation of input points, (2) generating a Voronoi diagram of input points by utilising the properties of Delaunay triangulation, and (3) extracting the triangles on the shape boundary, defined by input points, after selecting the tetrahedra which are contained inside the shape using the properties of Voronoi diagrams. The proposed method in this paper has some advantages compared to the previous approaches. First, the distance parameter, such as α in the α-shape approach, is not required in the proposed approach. The determination of a proper parameter by trial and error is not appropriate, especially in the automation of shape reconstruction. Secondly, the time complexity of the proposed approach is O(n) since, in a single pass, this algorithm determines whether each tetrahedron is located inside or outside the shape boundary. ID="A1"Correspondance and offprint requests to: Dr K. S. Kim, Department of Industrial Engineering, Pohang University of Science and Technology, San 31, Hyojadong, Pohang, 790–784, Korea. E-mail: kskim@postech.ac.kr  相似文献   

6.
Abstract

The force prediction is the precondition of improving equipment utilization ratio and optimizing process for CNC machining. Cutter-workpiece engagement (CWE) and in-cut cutting edge (ICCE) are the keys. In this article, a new analytic method of CWE and ICCE is proposed for ball end milling of sculptured surface and the prediction model of milling force is established. The sculptured surface is discretized into a series of infinitesimal inclined planes corresponding to cutter location points. The geometry relationships of cutter axis, feed direction and inclined plane are defined parametrically. The boundary curves and the boundary inflection points of the CWE are obtained by intersecting spatial standard curved surfaces with rotation transformation of coordinate system. The effective intersection points of the CWE and the cutter edge curve in Xc-Yctwo-dimensional plane are the upper and lower boundary points of ICCE. Based on the instantaneous chip thickness considering arbitrary feed direction, the force prediction model for ball end mill of three-axis surface milling is established. Simulation and experiment show that CWE and ICCE calculated by analytic method are well consistent with those of solid method. The predicted cutting forces match well with the measurements both in magnitude and variation trend.  相似文献   

7.
One objective of this work is to determine the optimal combination of the probe diameter and grid distance for freeform surface measurement, and another is to determine the optimal parameters for the local Shepard interpolation. The optimal combination of the probe diameter and grid distance for freeform surface measurement was determined through a Taguchi matrix experiment. The smaller the probe diameter and grid distance, the better the accuracy of the surface normal based on the configured matrix experimental result. The optimal parameters, namely the exponent and the radius R, for the local Shepard interpolation were determined by using the minimisation method of the root-mean-square normalised error (RMSNE) between the measured data points and the theoretical data points on a standard steel ball surface. The optimal parameters determined were actually applied to the measurement of a freeform surface (mouse surface) on a coordinate measuring machine (CMM). The local Shepard interpolation method was used to interpolate 16 control points from 1054 measured data points. Bi-cubic Bezier- and B-spline surface CAD models were constructed through these interpolated control points.  相似文献   

8.
This paper presents an investigation of the nonlinear least-squares sphere fitting algorithm (TLSA). The work concentrates on investigating the reliability of the TLSA algorithm when applied to a small segment angle of a sphere. The definition of small segment angle is discussed in the paper and taken to be below 1° (in both x and y directions) of the spherical surface. This application of the TLSA method is important when it is used on data from optical scanning systems where the measurements are limited by the gauge range and the angular tolerance of the sensor. The TLSA algorithm has been first compared with the TLSD algorithm suggested by Forbes for this application. The results show that the TLSA algorithm can be used in small surface segment angles. The main study is focused on testing the algorithm on a sphere superimposed with surface irregularities (sensor/measurement noise or roughness). Two properties of the TLSA algorithm are covered: the bias and the uncertainty of the estimated radius. Both simulation and theoretical approaches have been attempted. A new algorithm to estimate the bias of the TLSA algorithm has been derived in this paper based on Box's method. Together with uncertainty estimation, which can be produced by using either a conventional method or Zhang's error propagation function (EPF), a comprehensive understanding of the TLSA algorithm in this application is thus achieved, and used to develop a number of recommendations for the precision metrology of spherical and near spherical surfaces.  相似文献   

9.
The probability density function of the roughness height of a sliding surface is not always Gaussian like that of a truncated surface caused by running-in or mild wear. Therefore, it is important for obtaining contact pressure or frictional characteristics to estimate the truncation level of the non-Gaussian distribution function. This paper presents a method of determination of the two truncation parameters in the truncation model presented by King et al. [Proceedings of the 4th Leeds–Lyon Symposium on Tribology, MEP, London, 1978, p. 333]. The two truncation parameters p and β can be determined by plotting the values of skewness Sk and kurtosis K obtained from a measured profile of surface roughness on the SkK diagram calculated with the truncation model for various given values of parameters p and β. The height distributions reproduced by the truncation model with the truncation parameters p and β identified by the present method is in good agreement with the original ones of the measured surfaces.  相似文献   

10.
A laser sensor with multiple detectors for freeform surface digitization   总被引:3,自引:3,他引:0  
In this paper, an integrated laser scanning sensor for freeform surface digitization is presented. The sensor consists of a diode laser light source and four position-sensitive device (PSD) detectors. The stand-off distance of the sensor is 180 mm and the measurable range is 90 mm. The Lambert model is applied to calculate the displacement between the sensor and the measured point on the object surface along the optical axis, under the assumption of a diffusive surface. The inclination angle of the measured point from the vertical plane of the laser beam is calculated by mathematical inference. Those data are used in error compensation to improve the system precision. The new design of multiple detectors could increase the measurable angle and could solve the dead-space problem in the single-point laser of triangulation measurement. The computer simulation and actual measurements show that the displacement resolution is around 50 μm, and the system performs well in terms of stability and repeatability. The sensor system could be mounted on the NC machine or on the XY platform for freeform surface digitization.  相似文献   

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